Internal combustion engines are well known power generating devices which may have any number of differing configurations in dependence upon the type of fuel utilized, their size and the particular environment in which they are designed to operate.
Although several electronic fuel delivery systems for internal combustion vehicles are known to provide adequate performance characteristics, these systems tend to be expensive and do not address those motorized vehicles which include non-electronic fuel delivery systems. In those systems which utilize standard mechanical pumps for this purpose, there exists several inherent inefficiencies which the present invention seeks to address.
As can be seen in FIG. 1, a known fuel delivery system 10 of a typical high pressure, diesel engine utilizes a mechanical pump 12 (also referred to as a jerk pump or a block pump), and an unillustrated arrangement of camshafts and plungers, to intermittently provide a predetermined amount of fuel from a fuel supply 14 to a fuel injector 16 via an injection line. The nozzle of the fuel injector 16 operates to atomize the fuel as it enters the high pressure air combustion chamber of the engine.
In operation, pressure within the fuel injector 16 continues to build as the pump 12 provides fuel to the fuel injector 16 at the onset of a given fuel delivery cycle. A spring biased injector valve 22, typically a needle valve or the like of the fuel injector 16, opens in response to the pressure building within the fuel injector 16, thereby causing fuel to be dispensed through a series of passageways and into the vehicle's combustion chamber.
FIG. 2 is a graph illustrating the pressure at the nozzle portion of the fuel injector 16 during the fuel delivery cycle, wherein a slight drop in pressure can be seen to occur at the start of the injection process (in certain instances a slight change in the slope of the pressure curve may be seen, rather than an actual drop in pressure), although pressure continues to build at a desired rate after fuel injection has begun. Fuel will therefore continue to be delivered to the combustion chamber of the vehicle until the pressure within the fuel injector falls below the return spring biasing force of the injector valve 22. In these known systems, residual fuel which is left in the nozzle portion of the fuel injector 16 after the injector valve 22 closes is typically vented from the nozzle portion via a nozzle leak-off valve, conduit or the like. In other systems, such as that of the present invention, the residual fuel is not vented and remains in the line until the next injection.
In such systems as described in conjunction with FIGS. 1 and 2 above, the pressure of the fuel has a direct effect on how the fuel atomizes as it leaves the fuel injector 16 and enters the combustion chamber, and hence on how the fuel burns within the combustion chamber of the vehicle. Larger droplets of fuel are provided to the combustion chamber of the vehicle during those times when the pressure at the nozzle portion of the fuel injector 16 is comparatively low. These larger droplets tend to take longer to evaporate, mix and burn and therefore may not be able to completely combust within the combustion chamber before being exhausted therefrom. In addition, such large, low pressure and low velocity droplets may not make it to the distal side of the combustion chamber to mix with all the air. Such incomplete mixing and combustion aggravates pollution concerns, including the production of increased particulates, smoke, odor, hydrocarbons, carbon monoxide and the like.
It would therefore be advantageous to modify existing fuel delivery systems so as to reduce the generation of pollutants while increasing the efficiency of the fuel delivery system as a whole. Towards this end, the present invention seeks to raise the closing pressure of the injected fuel, while holding the starting pressure of the fuel injection at an elevated level.
It has been determined that by raising the closing pressure, the needle valve in the nozzles starts to close earlier as the pressure in the injection line begins to drop. The nozzle therefore tends to close completely before the line pressure goes to zero, thereby reducing the quantity of fuel injected at an undesirably low pressure. A problem exists in incorporating this pressure architecture with standard mechanical, or jerk, pumps because known mechanical pumps cannot reach the desired high opening and closing pressures to start at typical cranking speeds.
With the forgoing problems and concerns in mind, the present invention seeks to provide a controlled nozzle injection method and apparatus which operates in conjunction with known mechanical fuel pumps to reduce the amount of polluting contaminants emitted by an internal combustion engine.